Rename getSlug to slug

another 2 % of #2124
- renamed `/ghost/api/v0.1/posts/getSlug/ to
`/ghost/api/v0.1/posts/slug/`
- renamed method getSlug to generateSlug
Redirect feed -> rss

closes #2261

- reserved 'feed' in the list of reserved keywords for slugs
- added a 301 redirect from /feed/ to /rss/
- added a route test, and realised that standard express redirects don't get the right headers
- fixed the headers across all 301 redirects & added tests for the admin redirects
- removed the redirect from /ghost/login/ to /ghost/signin/ as this happens automatically if you're logged out, and isn't very useful if you're logged in as it just redirects again to /ghost/
Unlink import file when finished

fixes #2493
- Update db import version (in case it doesn't exist)
- Properly unlink file after import or error
Prevent adding duplicate tags with different casing

fixes #2478
- Check for existing tags with different case
Escape regex special characters in tag finder

refs #2149
- Properly highlight tags with special characters ($,[,],^,etc.)
Update some server side errors/warnings

issue #2482

- add help messages to all package.json errors/warnings
- change the pageUrl warning to have the correct version numbers
Merge pull request #2488 from ErisDS/issue-2261

Redirect feed -> rss
Fix delete button

closes #2492
- added when.all() to wait until all posts are deleted before deleting
tags
- added a test
Merge pull request #2494 from halfdan/2493-import-tmp

Unlink import file when finished
Merge pull request #2495 from halfdan/2478-tag-duplicate

Prevent adding duplicate tags with different casing
Merge pull request #2489 from ErisDS/user-msgs

Update some server side errors/warnings
Deduplicate upper-/lowercase tags for posts

server side check for #2478
- added check for duplicate tags in post model
Merge pull request #2497 from sebgie/issue#2492

Fix delete button
Merge pull request #2496 from halfdan/more-tag-fuddling

Escape regex special characters in tag finder
Ensure generateSlug gets transaction for tags

fixes #2460

- add transacting to tag saving
- add same to users while we're here
Merge pull request #2502 from ErisDS/issue-2460

Ensure generateSlug gets transaction for tags
Merge pull request #2498 from sebgie/duplicate-tags

Deduplicate upper-/lowercase tags for posts
Bump version to 0.4.2-rc2
Error handling for require-tree

fixes #2507

- ideally we would create an apps directory if one isn't present, but we can deal with that in later versions
Merge pull request #2508 from ErisDS/issue-2507

Error handling for require-tree